Targeted editing of nucleic acid sequences, for example, the targeted cleavage or the targeted introduction of a specific modification into genomic DNA, is a highly promising approach for the study of gene function and also has the potential to provide new therapies for human genetic diseases. Since many genetic diseases in principle can be treated by effecting a specific nucleotide change at a specific location in the genome (for example, an A to G or a T to C change in a specific codon of a gene associated with a disease), the development of a programmable way to achieve such precise gene editing represents both a powerful new research tool, as well as a potential new approach to gene editing-based therapeutics.